Ink jet nozzle method of manufacture

ABSTRACT

A nozzle array structure for pressurized fluid jets includes a uniform deposited membrane having an array of uniform small orifices therein overlaying a planar substrate having an array of larger aperture openings therethrough with approximately the same central axes as the orifice array. The method of making includes forming a substrate of a planar single crystal material oriented with the (100) planes parallel to the surface. A membrane comprising a uniform coating of an inorganic material is applied to the planar surface of the substrate. The substrate is preferentially etched from the rear surface to form an array of openings therein extending therethrough to the membrane. The membrane is then selectively eroded to form an array of uniform small orifices therein.

This is a continuation of application Ser. No. 665,143 filed Mar. 8,1976, now abandoned, which is a division of application Ser. No. 537,795filed Dec. 31, 1974, now U.S. Pat. No. 3,958,255.

BACKGROUND OF THE INVENTION

The need for high-quality, top-speed computer printers and other typesof output printers with changeable formats has been evidenced in recentyears. Developments have proceeded with respect to ink jet technology toanswer this need. Most developments in the field of ink jet have relatedto pressure deflected systems such as taught by Sweet U.S. Pat. No.3,596,275, wherein a single stream of ink droplets are selectivelycharged and passed through a uniform deflection field to impact variouslocations on a recording medium in accordance with the charge of eachdroplet. Thus, by applying suitable charging signals to the droplets, avisible human-readable printed record may be formed on the recordingsurface. This type of system requires very precise control over thecharge placed on each droplet due to various factors such as thetendency of similarly charged droplets closely adjacent to one anotherto repel each other and therefore impact the recording medium atunintended locations. The circuitry required to accomplish this precisecontrol appears to be relatively expensive, especially when duplicatedfor each jet of a multi-jet printer, which is required to attain trulyhigh speeds.

Another type of ink jet printing has been developed which offers thepotential of attaining high-speed, high-quality variable printingwithout requiring the expensive precision charging control electroniccircuitry. This type of printing may be called the binary pressure typeand is shown in Sweet et al, U.S. Pat. No. 3,373,437. This type ofsystem generates a plurality of jets in one or more rows, selectivelycharging drops with a single charge signal for deflection by a constantfield to an ink drop catcher. The uncharged drops continue along theoriginal jet stream path to impact a recording medium. The precisioncontrol over charging is not required inasmuch as charged drops impactthe gutter and not the recording medium. In the absence of selectivedeflection, the major disadvantage of this type of ink jet printing hasbeen that one nozzle is required for each printing position across theentire dimension of the path to be printed in a single pass. Thisrequires the fabrication of a vast number of nozzle orifices for asingle printer. Examples of ink jet heads designed for this type ofprinting are Beam et al U.S. Pat. No. 3,586,907 and Mathis U.S. Pat. No.3,701,998. A method for fabrication of orifices with this type of inkjet head is shown in Taylor U.S. Pat. No. 3,655,530. This methodinvolves the electroplating of the interior of predrilled holes untilsufficient material has been plated thereon to reduce the orificediameter to the desired size. This type of fabrication does not appearto lend itself to an extremely closely spaced linear array of orifices.

High quality printing requires that the individual drops and the spotsresulting from impact of the drops on the recording medium besufficiently small and closely spaced so as to be relativelyindiscernible as individual drops, but rather discernible only as partof the resultant printed symbol. This may require the printing of 200 ormore drops to the linear inch, each spot being approximately less thanseven mils in diameter. To achieve this arrangement with a double rowhead, wherein the orifices of one row are interleaved with respect tothe orifices of the other row as shown in above U.S. Pat. No. 3,701,998,would require orifices no larger than two mils in diameter to be spacedno wider than ten mils from center to center along a single row.

An object of the present invention is to provide an ink jet nozzlestructure having an extremely closely spaced array of small orifices.

Another object of the present invention is to provide a method formaking an ink jet nozzle structure having a closely spaced array ofsmall orifices.

A major difficulty involved is the fact that the ink or fluid to formthe jet must be pressurized and forced through the orifices atrelatively high velocities. Any ink jet nozzle structure must thereforebe constructed to withstand such pressure and velocities over a longperiod of time without significant wear or cracking over an extendedperiod of time.

SUMMARY OF THE INVENTION

Briefly, a multi-orifice nozzle array structure is provided forpressurized fluid jets. The structure includes a deposited membrane ofrelatively uniform thickness and having an array of uniform smallorifices therein, the membrane comprising an inorganic material. Thedeposited membrane overlays a planar substrate having an array of largerdiameter entrance openings therethrough with approximately the samecentral axes as the orifices. The method of making the multi-orificenozzle array structure includes forming a planar single crystalsubstrate oriented with the (100) planes parallel to the surface. Themembrane, comprising a uniform coating of an inorganic material, is thenapplied to the planar surface of the substrate. The substrate ispreferentially etched from the rear surface to form an array of openingstherethrough extending to the membrane, the etchant having a minimaleffect on the membrane. The membrane is then selectively eroded to forman array of uniform small orifices therein, each communicating with acorresponding entrance opening in the substrate and having approximatelythe same central axis therewith. By having a membrane, various orificeopening techniques may be employed for batch fabrication ofmulti-orifice nozzle arrays.

A feature of the subject invention is that the nozzle array may also beemployed with multi-orifice ink jet systems wherein drops areselectively deflected by a switchable deflection field rather than byselective charging. An example of such a system comprises Dill et alU.S. Patent Application Ser. No. 485,409 entitled "Method and Apparatusfor Recording Information on a Recording Surface," now U.S. Pat. No.3,992,712 which describes a multi-orifice magnetic ink jet system.

Another feature of the present invention is that it may be employed as anozzle plate in either the forward or reverse direction. When in thereverse direction, the structure is less affected by imperfections,defects, or residues, and is mechanically stronger.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portion of the nozzle plate structureof the present invention.

FIG. 2 is a schematic showing of an ink jet head structure incorporatingthe nozzle plate of the present invention.

FIG. 3 is a flow diagram in cross section, illustrating the steps forfabricating the nozzle plate of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT

Multi-orifice binary pressure ink jet systems offer the potential ofavoiding the extensive and costly charging control or deflection controlmechanisms of pressure deflected ink jet systems. The major difficultyof the multi-orifice binary pressure systems is the nozzle platestructure which must comprise a series of rows of closely spaced smallorifices which are uniform, resistant to cracking under pressure, andresistant to wear from the ink expelled at high velocity through theorifices. It is this problem that is solved by the structure of thepresent invention, which is manufacturable by batch fabrication.

Referring to FIG. 1, a portion of the nozzle plate of the presentinvention is illustrated schematically as viewed from the rear.Specifically, a substrate 20 is illustrated having a uniformly spacedarray of uniform openings 21 therethrough. The openings extendcompletely through the substrate to an inorganic membrane 22. Themembrane is punctured by a uniform array of uniform orifices 23. Theorifices are arranged in the same linear array as the openings 21 andeach orifice is approximately centered about the same central axis asthe corresponding opening 21.

As an example of a specific configuration, the silicon substrate may beabout 10 mils in thickness and the membrane 22 may be about 0.2 milthick. The intersection of opening 21 with membrane 22 along lines 24may form an opening of approximately 2 mils. In such a configuration,the diameter of orifice 23 may be as small as 0.4 to 0.5 mils. Thespacing of orifices 23 is dependent upon the expected coverage of thespots generated by the ink jet drops and by the number of rows oforifices, but the orifices in a single row may be compacted to within adistance of 5 mils from center to center.

With a substrate of single crystal silicon and a membrane of silicondioxide (SiO₂), the average burst pressure has been calculated to be15,000 PSI.

By means of the at least approximately 4 to 1 ratio between the width ofopening 21 and intersection 24 and the diameter of orifice 23, thenozzle aspect ratio becomes the ratio of the thickness of membrane 22vs. the diameter of hole 23. In the given example, the aspect ratio oforifice 23 is on the order of 0.5:1. As disclosed in Gordon U.S. Pat.No. 3,823,408, aspect ratios on the order of 0.5:1 have proven highlyadvantageous.

The nozzle plate of FIG. 1 is shown in FIG. 2 mounted in an ink jet headstructure. Reference numeral 25 denotes the nozzle plate of FIG. 1. Itis mounted in a head support structure 26 which encloses an ink manifoldand includes a vibrating mechanism 28 such as a piezoelectric crystal ormagnetostrictive transducer or the like mounted at the rear of thesupport structure. The chamber 22 has a supply tube 29 connected theretofor supplying the ink to the chamber under a suitable pressure, such as80 PSI. The head support structure 26 includes a shoulder potion 30 toprovide a seat for the nozzle plate 25, which may be secured to thesupport structure by cementing along the frontal edge 31. The ink underpressure in the cavity 27 is perturbated by transducer 28 so as tosynchronize the formation of drops by the jet streams emanating fromorifices 23 at a uniform frequency and predictable phase and size.

The substrate 20 of nozzle plate 25 has been found to be best formedfrom single crystal silicon. The membrane 22 may be made of severalmaterials, such as silicon dioxide (SiO₂), glassy materials such as"Pyrex", polycrystalline silicon, silicon nitride, or other suitablematerials.

FIG. 2 illustrates nozzle plate 25 emplaced in the forward direction. Incertain circumstances, such as high pressure, e.g. 120 PSI, usage, it isadvantageous to emplace the plate 25 in the reverse direction. When inthe reverse direction, the structure and the resultant ink jet are lessaffected by imperfections, defects, or residues behind the orifice.Since the monocrystalline silicon is not in contact with the ink, thestructure additionally is able to better resist etching by the ink. Thestructure is also mechanically stronger. However, the anisotropicallyetched substrate does not present a smooth surface on which may beplaced circuitry, for example, for drop synchronization.

FIG. 3 illustraes the method of making the nozzle plate 25. Generally,the method of making the nozzle plate 25 comprises providing a substrateof a single crystal material, such as silicon, oriented with the (100)planes parallel to the surface, as shown in Step A. A membranecomprising a uniform coating of an inorganic material is applied to theplanar surface of the substrate as shown in Step B. Steps C and Dcomprise the anisotropic etching of the substrate from the rear surfaceto form an array of openings therein extending to the membrane 22. Inthis description, the words "anisotropic" and "preferential" are usedinterchangeably, having the same meaning. Steps E and F illustrate theselective erosion of the membrane 22 to form a uniform array of smallorifices 23 each having their central axis approximately concentric withthe central axis of the opening 21.

More specifically referring to FIG. 3, Step A comprises the provision ofa monocrystalline silicon substrate slice having a (100)crystallographic orientation. Techniques for providing a semiconductorslice of this type are well known and need not be specifically describedfor purposes of the present disclosure.

Step B comprises the provision of the membrane layer of about 0.2 milthickness on the substrate 20. Various materials may be utilized asdiscussed above. If silicon dioxide or silicon nitride is used as themembrane material at 2 to 6 microns in thickness, it is preparedpreferably either by chemical vapor deposition, by sputter deposition,or as a thermally grown oxide. Each of these processes is well known inthe art and need not be specifically described here. The polycrystallinesilicon membrane is best prepared by chemical vapor deposition or byelectron beam deposition. Again, these techniques are well known in theart. The "Pyrex" film membrane is preferably formed by sputterdeposition.

Steps C and D represent the formation of the aperture holes 21 in themonocrystalline substrate. A suitable mask material 35 may be formed inStep C to control the location and orientation of the etching of thesubstrate in step D. The entrance holes 21 are preferentially etched inthe (100) single crystal silicon using a water amine pryocatecholetchant or other basic etchants. It has been known for some time thatthe (111) plane is a slow etch plane in single crystalline siliconmaterial. Thus, the etching of Step D produces a pyramidal hole in thesubstrate having as its surface the (111) plane. The pyramid becomestruncated upon encountering the membrane 22 as the etching expands thepyramid laterally. The precision etching of monocrystalline materials inthis manner is now an established technique and is discussed extensivelyin the art, for example, in Kragness et al U.S. Pat. No. 3,765,959.

Preferential etching is also discussed in the article by Sedgwick et al,Journal of the Electrochemical Society, Vol. 119, No. 12, Dec. 1972,entitled "A Novel Method for Fabrication of Ultrafine Metal Lines byElectron Beams."

Steps E and F represent formation of the orifices 23 in the membrane 22by chemical etch, sputter etch, ion etch or plasma etch through anappropriate selection of photoresist mask and/or metal mask 36. Electronbeam lithography may be used in place of conventional photolithographywhere the resolution or definition of the orifices 23 becomes extremelycritical. Photolithographic masking and etching techniques are wellknown and conventional and need not be discussed here.

By having a membrane in conjunction with a substrate, various orificeopening techniques can be employed for batch fabricating reproduciblemulti-orifice nozzle arrays. Batch fabrication refers to thesimultaneous production of several sets of nozzle plates on a singleand/or several wafers. For example, chemical etching is preferred forthe silicon dioxide membrane, and plasma etching or reactive sputteretching is preferred for the silicon nitride membrane. Both theseapproaches lend themselves to batch fabrication in reproduciblemulti-orifice nozzle arrays.

From the above description it is apparent that a new nozzle plate isprovided which is usable for high-quality, high-resolution andhigh-speed ink jet printing of the binary pressure type.

While the invention has been particularly shown and described withreference to a particular embodiment thereof, it will be understood bythose in the art that the above and various changes in the form anddetails may be made therein without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A method of fabrication of a multi-orifice nozzleplate for pressurized fluid jets a monocrystalline substrate with anarray of entrance openings overlayed by an inorganic membrane with anarray of orifices corresponding with said openings, said methodcomprising the steps of:forming a layer of inorganic membrane materialof uniform thickness less than one mil on the front surface of saidmonocrystalline substrate; said inorganic membrane material havingphysical characteristics sufficient to withstand said pressurized fluid;controlled chemical preferential etching said monocrystalline substratefrom the rear surface to form an array of uniform openings therethroughto said membrane; and etching said membrane to form an array of uniformorifices therethrough, each of said orifices communicating with one ofsaid substrate openings having approximately the same central axistherewith, and having smaller areal cross sections than said substrateopenings.
 2. The method of claim 1 wherein:said monocrystalline subtrateis silicon; and including the additional first step of orienting saidsubstrate such that said front and rear surfaces are parallel surfacesoriented in the (100) crystallographic direction of said substrate. 3.The method of claim 2 including the additional step of masking saidsubstrate on said rear surface in a suitable manner such that saidchemical preferential etch step forms said entrance openings in a squarefrusto-pyramidal shape having sides oriented in the (111)crystallographic direction of said substrate.
 4. The method of claim 3including the additional step of masking said membrane to control thelocation and dimensions of said membrane etching step.